1. Field
The present disclosure relates generally to composite structures and, in particular, to a method and apparatus for reworking an area on a composite structure. Still more particularly, the present disclosure relates to a method and apparatus for fabricating a patch in a rework area on a composite structure.
2. Background
Aircraft are being designed and manufactured with greater and greater percentages of composite materials. Composite materials are used in aircraft to decrease the weight of the aircraft. This decreased weight improves performance features, such as payload capacities and fuel efficiencies. Further, composite materials provide longer service life for various components in an aircraft.
Composite materials are tough, light-weight materials that are created by combining two or more functional components. For example, a composite material may include reinforcing fibers bound in a polymer resin matrix. The fibers may be unidirectional or may take the form of a woven cloth or fabric. The fibers and resins are arranged and cured to form a composite material.
Further, using composite materials to create aerospace composite structures potentially allows for portions of an aircraft to be manufactured in larger pieces or sections. For example, a fuselage in an aircraft may be created in cylindrical sections and then assembled to form the fuselage of the aircraft. Other examples include, without limitation, wing sections joined to form a wing or stabilizer sections joined to form a stabilizer.
In manufacturing composite structures, layers of composite material are typically laid up on a tool. The layers may be comprised of fibers in sheets. These sheets may take the form of fabrics, tape, tows, or other suitable forms. In some cases, resin may be infused or pre-impregnated into the sheets. These types of sheets are commonly referred to as prepreg.
The different layers of prepreg may be laid up in different orientations, and different numbers of layers may be used, depending on the thickness of the composite structure being manufactured. These layers may be laid up by hand or by using automated lamination equipment, such as a tape laminating machine or a fiber placement system.
After the different layers of composite material have been laid up on the tool, the layers of composite material may be consolidated and cured upon exposure to temperature and pressure, thus forming the final composite structure. Thereafter, the composite structure may be inspected to determine whether inconsistencies are present. The inspection may be performed using x-ray inspection systems, ultrasound inspection systems, and other types of non-destructive inspection systems.
If an inconsistency is identified, the composite structure may be reworked. In some cases, the inconsistency may result in the composite structure being discarded, thus requiring a new composite structure to be manufactured. Examples of inconsistencies that may be present in a composite structure include voids, porosity, delamination, foreign object debris (FOD), and other types of inconsistencies.
In reworking a composite structure with an inconsistency, layers of composite material are removed from an area in which the inconsistency is located. The layers may be removed until the inconsistency is also removed from the composite structure. The removal of the layers of composite material results in a scarf in which the layers of composite material are exposed.
A patch is fabricated to fill the scarf in performing the rework. The patch includes plies of composite material. These plies have sizes that match the layers removed from the composite structure. Further, the plies for the patch also have the same orientations as the layers of composite material removed from the composite structure.
In fabricating a patch, a transparent sheet of material is placed over the rework area in which the layers of composite material have been removed. Layer boundaries are present for the exposed layers in the rework area. These layer boundaries are traced onto the transparent sheet to form a transparency. Additionally, the orientation of the exposed layers may be marked on the transparency. This transparency containing the layer boundaries and other markings is a master transparency.
Thereafter, a new transparent material is placed over the master transparency. One of the layer boundaries is traced onto a new sheet of transparent material to form a transparency for an individual ply that is to be formed. In this manner, transparencies are created for each of the plies that are to be cut from a composite material for a patch.
If multiple patches are needed, additional sets of transparencies are made from the master transparency. Additional patches may be fabricated to perform testing prior to the actual installation of the patch into the rework area. For example, a thermal survey may be performed with one copy of the patches prior to the installation of another copy of the patches in the rework area.
Thereafter, each of the transparencies is overlaid onto a layer of material. This layer of material is a layer of composite material, such as a carbon fiber fabric. The transparencies are overlaid onto the layer of material with a desired orientation. Thereafter, plies are cut out from the transparencies and overlaid onto the material. These plies may then be placed into a stack to form the patch.
These different steps are currently performed by a human operator. As a result, transparencies that are created from the master transparency may not all have the same measurements as the master transparency because of errors in tracing. Additionally, having a human operator cut the layer of material also may result in a ply that does not match the transparency as closely as desired.
These copying and cutting errors may result in a patch that does not properly fit the rework area. As a result, the process may be repeated again, the composite structure may be discarded, or some other operation may be needed to perform a rework of the composite structure.
As a result, this type of process may be more time-consuming and expensive than desired when a patch cannot be used, and the process is performed again to fabricate a new patch. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method and apparatus that overcome a technical problem with fabricating patches in a manner that reduces copying and cutting errors.